Production of gas mixtures containing carbon monoxide and hydrogen



Oct. 2, 1956 H. z. MARTIN ETAL PRODUCTION OF GAS MIXTURES CONTAININGCARBON MONOXIDE AND HYDROGEN 4 Sheets-Sheet 1 Original Filed April 2,1946 M me 3 Q M W on $7 i l /Z gg e'nbors bagd abbot-neg Oct.'2, 1956 H.z. MARTIN ETAL 2,765,222

PRODUCTION OF GAS MIXTURES CONTAINING CARBON MONOXIDE AND HYDROGENOriginal Filed April 2, 1946 4 Sheets-Shet 2 T FaoM Cooune o CQOLIN TowEAL TOWEK SLURB-Y Reruns Homer '2. martin I ram snverzoor's batter-neg Ot- 1956 H. z. MARTIN ETAL 2,765,222

PRODUCTION OF GAS MIXTURES CONTAINING CARBON MONOXIDE AND HYDROGENOriginal Filed April 2, 1946 4 Sheets-Sheet 3 ------flir------fllCONDENSATE 54.5 5 .5

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PRODUCTION OF GAS MIXTURES CONTAINING CARBON MONOXIDE AND HYDROGEN oriinal Filed April 2, 1946 4 Sheets-Sheet 4 a GAS Qaoxnmzan.

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gMCLL/borneg United States atent PRODUCTION OF GAS MIXTURES CONTG CARBONMON OXIDE AND HYDROGEN Homer Z. Martin, Cranford, and Frank T. Barr,Summit, N. J., assignors to Esso Research and Engineering Company, acorporation of Delaware Original application April 2, 1946, Serial No.659,941.

Divided and this application December 15, 1951, Serial No. 261,896

4 Claims. (Cl. 48196) This application is a division of Serial No.659,041, filed April 2, 1946, and now abandoned, for Oxidation Process."

This invention relates to the oxidation of gaseous hydrocarbons such asnatural gas, methane, or the like. More particularly, the invention isconcerned with the oxidation of such gaseous hydrocarbons by means ofmetallic oxides to form mixtures of hydrogen and carbon monoxidesuitable for the catalytic synthesis of hydrocarbons.

The use of metallic oxides as the source of oxygen in the oxidation ofgaseous hydrocarbons has been proposed before. Experience has shown thatwhen the reaction is conducted by passing the hydrocarbons through afixed bed of the heated metallic oxide, the extent of the reaction isditficult to control as a result of the excess of oxygen which isavailable for reacting with the incoming feed and the poor distributionand transfer of heat throughout the solids bed. The reaction usuallyproceeds until the oxidation reaches its farthest stage to formexclusively carbon dioxide and water instead of the desired loweroxidation products such as oxygenated organic compounds or mixtures ofcarbon monoxide and hydrogen. This difficulty can be avoided by the useof certain metal oxides such as zinc oxide which have relatively lowoxygen vapor pressures. However the use of these oxides generallyinvolves other serious disadvantages such as low sublimation or meltingtemperatures. Attempts have been made to overcome these difiiculties bysuspending controlled amounts of finely divided metal oxides in aspecific volume of gaseous hydrocarbon to be oxidized and passing thissuspension through a reaction zone at controlled reaction conditions.While this method avoids some of the drawbacks of fixed bed operationnew dithculties arise particularly in the manufacture under pressure ofmixtures of carbon monoxide and hydrogen suitable for the hydrocarbonsynthesis.

The hydrocarbon synthesis, particularly its high pressure modificationcarried out in the presence of iron catalysts has assumed considerableimportance in recent years because of its relatively high yields ofanti-knock motor fuels. An efiicient and economic operation of thisprocess requires the production and supply of the synthesis feed gas atabout the pressure at which it is converted in the synthesis reaction.Production of synthesis gas by the oxidation of methane with metaloxides under pressure involves the regeneration of the reduced metaloxide by oxidation with air. When metal oxides suspended in the reactinggas are used for this reaction they must be separated from the gaseousreaction product, reoxidized in a separate regeneration zone andreturned to the reaction zone. The regeneration zone must either beoperated at the same pressure as the reaction zone or finely dividedsolids must be conveyed from a low pressure zone to a high pressurezone. In the first case, large volumes of air required for regenerationhave to be compressed to the reaction pressure which is a highlyexpensive procedure. In the latter case special pressur- Fatented Get.2, i956 ized means of conveyance are required which, particularly whenpressures of about 100 pounds per square inch, or above are used,involve high investment cost and considerable operating difficulties.The present invention overcomes these difiiculties and atfords variousadditional advantages, as will appear from the following descriptionthereof read with reference to the accompanying drawing which showssemi-diagrammatic views of apparatus adapted to carry out preferredembodiments of the invention.

It is therefore the principal object of our invention to provide animproved process for oxidizing hydrocarbon gases with the aid of finelydivided metal oxides at a controlled rate of reaction.

A further object of our invention is to provide an in proved method ofconverting methane with the aid of finely divided metal oxides into gasmixtures containing carbon monoxide and hydrogen.

A more specific object of our invention is to provide a process of thetype specified which will permit oxidation of the hydrocarbons andregeneration of the metal oxide at different pressures without requiringsubstantial compression of air or complicated conveying means forpowdered solids.

Other and further objects and advantages will appear hereinafter.

In accordance with one embodiment of the present invention, finelydivided metal oxide of a suitable oxygen partial pressure is maintainedwithin a treating zone in the form of a dense bed of solids fluidized bysmall amounts of an aerating gas to form a well defined upper level andto exert a pseudo-hydrostatic pressure on its base. Controlled amountsof finely divided metal oxide of a suitable oxygen partial pressure arepassed under the pseudo-hydrostatic pressure of said dense bed to areaction zone through which the gases to be oxidized flow continuouslyat a superficial velocity sufficient to carry the metal oxide particlesintroduced into the reaction zone along in the form of a solids-in-gassuspension of a density substantially lower than the density of saiddense bed. The temperature, pressure and residence time of this lowdensity suspension in the reaction zone are so controlled as toaccomplish the desired degree of oxidation. The suspension of reducedmetal oxide in reaction products is passed into a separation zone fromwhich the desired oxidation products are recovered and reduced metaloxide is returned to said dense bed.

The treating zone containing the dense bed and the connecting linesbetween the treating and the reaction zones may be maintainedsubstantially at the pressure of the reaction zone. This procedure maybe continued until the bulk of metal oxide in the dense bed has lostmost of its oxidizing strength, whereupon the fiow of solids from thedense bed to the reaction zone is interrupted, the pressure on the systmis released, and air is passed upwardly through the dense bed at atemperature adapted to regenerate the metal oxide to its original stateof oxidation. The superficial velocity of the air is preferably socontrolled that the dense phase is maintained in a state of highturbulence resembling a boiling liquid retaining a well defined upperlevel from which only minor portions of the solids are entrained andcarried out of the dense phase by the air stream. When the regenerationis completed the system is placed back on stream and under pressure fora new reaction cycle. Two or more systems of this kind may be providedto insure a continuous flow of the desired oxidation products. It willbe appreciated that in this manner the oxidation reaction may be carriedout at any desired elevated pressure without requiring the compressionof large amounts of regeneration air or pressurized solids-conveyingmeans.

We prefer to maintain relatively large amounts of metal oxide in thedense bed as compared with the amount of metal oxide suspended in thereaction zone at any one time in order to extend the duration of thereaction period between periods of regeneration. In general, thediameter of the reaction zone will be susbtantially smaller than that ofthe dense phase zone, say about to preferably about /3 the diameter ofme latter to facilitate the formation of the low density suspension attechnically feasible space velocities. The metal oxide and the gas to beoxidized are carried through the reaction zone at such a velocity thatboth materials are continually moving in the same direction with littleor no back-mixing of the gas, and the conditions should be such that theoxidizable gas moves forward at least as rapidly as the oxide. In thismanner it is possible to definitely limit the amount of oxygen whi h issupplied to a given quantity of the hydrocarbon gas Within the reactionzone. 'Thus, the oxidation reaction may be controlled by simplycontrolling the amount of oxide which is reacted with a given amount ofgas to be oxidized.

The heat balance of our process depends largely on the heats offormation of the metal oxide and hydrocarbon used as compared with theheat of formation of the desired oxidation products. For example, in theproduction of carbon monoxide and hydrogen from methane the heatgenerated by the exothermic formation of carbon monoxide is in generaltheoretically deficient to decompose the methane and reduce the metaloxide. Additional heat may supplied to this reaction by controlling theoxidation reaction so that small amounts of carbon dioxide and water areformed in a more strongly exothermic side reaction. However, a morepreferred means of supplying additional heat of reaction is given by thestrongly exothermic regeneration reaction whose heat may be transferredto the reaction zone as sensible heat of the metal oxide or by any otherconventional means of heat recovcry and transfer.

It is a particular advantage of our invention that the reaction andregeneration temperatures may be controlled with the greatest of ease.The reaction temperature may be maintained at an optimum level bycontrolling the amount of solids supplied to the reaction zone while theregeneration temperature may be readily kept within the desired range bycontrolling the amount of air supplied, and if necessary, byconventional cooling means contacting the dense solids phase. The oxygencontent of the solids circulated to the reaction zone may be socontrolled that any desired proportion of these solids may act as inertheat carriers.

According to a more specific modification of this embodiment of theinvention We may use the separate reaction zone merely during theearlier stages of the production period until the oxygen concentrationof the bulk of metal oxide in the dense phase zone is reduced to a levelat which the danger of over-oxidation of the hydrocarbon gas issusbtantially diminished or entirely removed. Thereafter the feed gas tobe oxidized may be passed directly through the dense bed of metal oxideat a rate adapted to accomplish the desired oxidation. Our inventionalso includes the introduction of small amounts of hydrocarbon gas intothe dense phase during the regeneration period to supply additional heator preheat for the regeneration reaction, if desired. For example, thedepressurized gas obtained from the reaction zone at the end of theproduction period is suitable for this purpose.

The metal oxides which may be used in the present process are quitegenerally such oxides as have such an afiinity for oxygen at thetemperatures of our process that their oxygen partial pressures atequilibrium with both higher and lower stages of oxidation present areless than about 0.10 atmosphere and preferably less than 0.01 atmosphereso that substantially all the oxygen of the air used for regenerationcan be bound by the lower stage of 4 oxidation. The metal oxides shouldalso be capable of oxidizing the hydrocarbon gas at least to carbonmonoxide and hydrogen at the temperatures and pressures of theoperation.

They may also have a catalytic activity for the oxidation reaction.While certain oxides which are reduced to metals, such as ferrous oxide,cuprous oxide, andthe like, are useful for our process, other suitableoxides are the higher oxides of metals which are capable of forming bothhigher and lower oxides. Typical of these other suitable oxides are:cupric oxide, vanadium pentoxide, ferric oxide, and stannic oxide.Suitable also are mixtures of these oxides and mixtures with a suitablecarrier such as kieselguhr. The use of carriers consisting of adsorbentmaterials for the oxide is especially advantageous in that it helps tobring the oxidizable substance and the oxide into close contact and tomaintain such contact throughout the reaction zone. Suitable carriersare alumina or silica gels, bentonites, kieselguhr and the like. inaddition to the pure oxides, mixtures of oxides with finely dividedmetal catalysts may also be used, such as a mixture of nickel withvanadium pentoxide, which may have reforming activity to convert methanewith CO2 formed in the process into carbon monoxide and hydrogen.

enever mixtures of metal oxides and reforming catalyst are used for theconversion of gaseous hydrocarbon into carbon monoxide and hydrogen inany process involving the reoxidation of the metal oxidecatalyst mixturewith air, it is desirable that the solids in the methane reaction zonecontain little or no reformer catalyst in the inactive oxidized state.We have found that this condition may be complied with if the oxygenbearing metal has a lower vapor pressure of oxygen than,

that of the oxidized reformer catalyst. For example if CuzO is the oxideused to carry oxygen to the methane reaction zone, operation with nickelreforming catalyst will be satisfactory. The CuzO has a vapor pressureof oxygen equal to 2.5 l0- atmospheres. This vapor pressure issutficiently high to carry out the oxidation reaction required in themethane contactor. The nickel oxide, if formed, has a vapor pressure ofabout 0.001 atmosphere or greater at conditions in the reoxidizer whichmay be around 1700 F. for example. Thus, if nickel oxide is formed inany part of the reoxidizer it would tend to give up its oxygen to thecopper metal which may be present in excess. Another metal. oxide whichmay be used successfully in this manner is Fe3O4. In general wecontemplate the use of those metal oxides whose vapor pressures ofoxygen are lower than that of nickel oxide or the oxidized state of anyother reforming catalyst used. A pressure of steam in the oxidizer andsolids return leading to the methane reaction zone may be helpful; itmay react with the reduced metal to form H2 and CuzO and the formerreduces the reforming catalyst. Good results have also been obtainedwith mixtures of copper oxide with about 5-50% of iron oxide, to which areforming catalyst such as nickel is added.

For the purpose of maintaining the required velocity of the oxide in thereaction zone it is desirable that the oxides be used in a powdered orgranular form and that the granules be at least as small as mesh. It isalso desirable that not more than 25% of the mass of the oxide consistof material finer than 325 mesh. In general, it is preferred to usematerial within the range of 200 to 400 mesh. When using oxide particlesof such dimensions the velocity within the reaction zone should be from1 to 30 ft./sec., preferably about 2-5 ft./s ec., in order to maintain acontinuous forward flow of both oxide and oxidizable material withoutpermitting extensive backmixing of the gas. The dense metal oxide phasemay be suficiently fluidized during the reaction period by small amountsof an inert aerating gas, preferably steam. The superficial velocity ofthe air blown through the dense phase during the regeneration period isgenerally maintained between the approximate limits of 0.3-3 ft./sec.,preferably about 12 ft./sec.

In accordance with another embodiment of the present invention a portionof the total amount of gaseous hydrocarbon used may first be reactedwith a metal oxide such as copper or iron oxide to form substantialproportions of carbon dioxide and water, and, possibly also carbonmonoxide and hydrogen, and the exit gas of this reaction may be reactedwith the remainder of the gaseous hydrocarbon in a reforming zone in thepresence of a reforming catalyst such as nickel to complete theconversion of the feed gas into carbon monoxide and hydrogen byreformation. In this case, as in the embodiment described before, thereoxidation of the metal oxide may be carried out in a separate vesselat a pressure substantially lower than that of the oxidation and/orreformation of the feed gas.

Having set forth the general nature and objects, our invention will bebest understood from the more detailed description hereinafter, in whichreference will be made to the accompanying drawing in which:

Figure l is a semi-diagrammatic view of apparatus suitable to practice apreferred embodiment of the invention.

Figures 2 and 3 are diagrammatic views of apparatus for treatin theproduct gases and Figure 4 is a diagrammatic view of an apparatusadapted to carry out another specific embodiment of our invention.

Referring now in detail to Figure 1, the system illustrated thereinessentially comprises two dense phase chambers, 1-9 and 59, eachconnected to a dilute phase reaction chamber, 39 and 70, respectively,and each including a reaction tube or tubes, 49 and 80, respectively,the functions and cooperation of which will be forthwith explained.While the conversion of natural gas to a mixture of carbon monoxide andhydrogen suitable as a feed gas for the catalytic synthesis ofhydrocarbons will be described for purposes of illustration, it shouldbe understood that the system is readily adaptable to other controlledoxidations of gaseous hydrocarbons.

To start up the process, air of substantially atmospheric pressure,which may be preheated to a temperature as high as about 1800" F. duringthe starting period is supplied by blower 1 through line 3 and valve 5to the lower portion of chamber 1! which it enters through a perforateddistribution plate or grid 8. A limited amount of a combustible gas,preferably natural gas from line 7 is added to the air to be burned andproduce heat within chamber 18. A bed of finely divided metal oxide, forexampl F30d or an iron ore such as hematite, having a particle size ofabout 100-200 mesh is arranged above grid 8 and fluidized by theupwardly streaming gases having a superficial velocity of about 1.5 ft./sec. to form in zone 12 a dense turbulent fluidized mass of solidsresembling a boiling liquid and forming a well defined upper level 14.Residual air and combustion gases are withdrawn overhead from densephase zone 12 to lose most of their entrained solids in the free space16 above level 14 and to be vented through valve 18 and line 20. Ifdesired, a conventional gas solids separator 17 of the centrifugaland/or electrical type may be arranged in the path of the outgoing gasand separated solids may be returned to the dense phase 12 through line19. The amount of combustible gas introduced into chamber is socontrolled that the desired amount of heat is produced withoutappreciable reduction of the iron oxide.

When the temperature of the dense phase 12 has reached a level betweenabout l400 and 1800 F., preferably about 1700 F., the gas flow is haltedby closing valves 5 and 9 and the gas to be oxidized, in this casenatural gas, available at a high pressure, is fed through lines 24 and26 to reaction chamber 36 which may have about /3 the diameter of densephase chamber 10. The oxidation reaction of the natural gas may becarried out under an elevated pressure such as 50 to 400 lbs. per sq.in, say at about 300 lbs. per sq. in. For this purpose,

valves 5, 9, 18, and 36 remain closed until the desired, pressure hasbeen built up in the system whereupon valve 36 is opened sufficiently torelease gaseous products at the operating pressure. The flow of naturalgas through chamber 33 is adjusted to a space velocity of about 50 to500 v./v./hr. and a superficial velocity of about 25 ft./sec. Hotfluidized F6304 is permitted to flow under the pressure of the densefluidized bed in zone 12 through line 33 and control valve 34 into line26 where it is picked up by the natural gas to form a dilute suspensionwhich is passed upwardly through chamber 30 and returned through line 32into chamber 16 above dense phase level 14.

The flow rate of F30 i through valve 34 is so controlled that an amountof oxygen is made available which is required for the conversion intocarbon monoxide and hydrogen of the amount of methane passing with thesolids through chamber 31 and that the reaction temperature is keptwithin the approximate limits of 14904000 R, preferably 1500-1800" F. Ingeneral, solids flow rates of about 5.0 to 25.0 lbs. per cu. ft. ofnatural gas supplied at standard conditions are adequate for thispurpose, using increasing rates as the cycle proceeds, so as to make upfor the decreased concentration of oxygen on the fluid solids in zone12. The flow condition in chamber 38 may be so controlled that thesolids have a slightly longer residence time in chamber 3i than the gasto establish the phenomenon of mild hindered settling.

A relatively dilute suspension of reduced FeaO4 in a mixture of carbonmonoxide, hydrogen, steam and unconverted natural gas enters the freespace 16 of chamber 10 wherein the superficial velocity of the gas is sodrastically reduced that most of the suspended settle out and drop backinto zone 12. Any solids remaining entrained may be removed in separator17 and returned to zone 12 through line 19. Product gas is withdrawnthrough line 35 and valve 36 and passed through line 33 to any dcsiredfurther treatment or the synthesis process.

When the oxygen content of the oxide in Zone 12 has fallen beneath anoperative concentration or the reaction temperature drops below thedesired level, valves 34 and 36 are closed, valve 18 is opened torelease the pressure to atmospheric, the flow of natural gas throughchamber 30 is halted and air is again admitted through line 3, ifdesired, admixed with small amounts of natural gas from line 7 toreoxidize and reheat the iron oxide to the desired degree at atmosphericpressure. ing this regeneration period rises too high, heat may bewithdrawn by means of cooling coil 42, to be used in any desired stageof the process. When the regeneration is complete the system is readyfor a new reaction cycle as outlined above.

In accordance with another modification of our invention the reactionchamber may have the form of one or more draft tubes 4% arranged withindense phase zone 12 of chamber 1b, to be used in place of chamber 34) inthe following manner. Tube or tubes 46 having a diameter of from aboutto the diameter of chamber 10 extend from a point close to the bottom ofzone 12 to a point above level 14. The upper end of the tubes is openwhile their lower end is provided with fixed or adjustable orifices 4iadmitting only a controlled amount of fluidized solids into tubes 40.During the production period natural gas is passed through line 39 intothe lower end of tubes 49 and is contacted only with the solids whichare induced to flow into the draft tubes as a result of the lowersuspension density in these tubes as compared with that of the densephase 12. In all other respects the operation of tubes 49 is the same asthat of reactor 39 as Will be readily understood by those skilled in theart.

In order to insure a continuous flow of product gas a second systemsimilar in construction and operation to that described above isprovided to be run on production and regeneration in periods alternatingwith the pro- If the temperature durduction and regeneration periods ofthe system described. For this purpose air is supplied from line 3through line and valve 47 to chamber 50 during the production period ofchamber 10. Natural gas may be added through lines 51 and 53 and valve55. Chamber 50 is provided with a grid 57 which supports a dense phase59 of finely divided oxide having an upper level 60. Gas solidsseparation takes place in space 62 and/or separator 64 provided withsolids return line 65. Spent regeneration gas is withdrawn through line67 carrying valve 68 and leading into line 20. Heat may be withdrawnfrom zone 5!) by means of cooling coil 86. The operation conditionsduring the regeneration period are the same as those outlined inconnection with the preheating and regenerating periods. of chamber 10.

During the regenerating period of chamber 19, chamber 50 is switched toproduction by closing valve 47, and 68, admitting natural gas throughline 69 to chamber 79, adjusting the pressure within the system with theaid of valve 72 on line 74 and admitting controlled amounts of H oxidefrom dense phase 59 through line 76 and control valve 77 to chamber 79.As an alternative, draft tube or tubes 80 provided with orifices 82 mayreplace chamber 79 using natural gas supply line 84 instead of line 69.Operation during the production period is as outlined above inconnection with chamber 10 and its accessories.

The embodiment of our invention illustrated by the drawing permits ofvarious modifications. A preferably inert fiuidizing gas, preferablysteam, may be introduced in small amounts into zones 12 and 59 duringthe production periods by way of line 88 via lines 90 and 92,respectively, in order to maintain the flow and hydrauliccharacteristics of the dense phases. A brief purging stage may followeach regeneration and production period using an inert gas such assteam, flue gas, etc., to prevent the formation of explosive mixtures ina manner known per se. The heat generated during the regeneration periodin one chamber may be utilized to supply heat to the reaction takingplace in another chamber, using any conventional heat transfer means notshown.

Cooling means may be provided to cool the hot exit gases leavingchambers 10 and 50 ahead of valves 18, 36, 68, and 72 and also ahead ofseparators 17 and 64 which in that case may be arranged outside chambers10 and 50 to prevent damage to these elements by overheating and topermit the use of less expensive construction materials therefor.

It may also be desirable to scrub the gases leaving the gas-solidsseparators 17 and 64 from any further entrained solids fines for whichpurpose liquid scrubbing zones using water or any other suitablescrubbing liquid may be arranged on the path of the exit gasessubsequent to the dry separation zone. Cooling and scrubbing of theexist gases may be accomplished simultaneously in these scrubbing zones.A scrubbing system particularly well adapted to this purpose as well asto recover solid fines from hot gas streams quite generally isillustrated in Figure 2.

Referring now in detail to Figure 2, gases which contain powdered solidsin a finely divided state and which may have a temperature of about400-800 F. enter tower 210 through. line 205. Water may be injectedthrough line 215 into the inlet gases, which by adiabatic evaporationcools the gases to the neighborhood of about 200300 F. A small quantityof water is then fed through line 220 to the top tray of a series of 2or 3 vaporliquid contacting zones, such as bubble trays 239 and thegases in passing countercurrently to this water are scrubbed of the dustparticles which they contain. It is noted that of the water sent to thetrays and into the inlet pipe, all but about vaporizes and this latterquantity is used to form the slurry by which the solids are removed fromtower 210 and in which they may be returned to the process. The cooledgases leave the top scrubber tray 230 and enter a cooling zone 240. Herea much larger quantity of water at about F. supplied from a coolingtower through line 245 is sprayed by sprayer 250, preferably overpacking material and the gases are cooled and dehumidified leaving in asaturated condition at l00200 F. at the top through pipe 255. The largequantity of water used in this step is withdrawn from a tray 261)through line 265 and recycled to the cooling tower through line 266. Aportion of this stream may be recycled directly to tower 210 throughline 268. The relatively small quantity needed in the lower part of thetower may be taken from the stream in 265, as indicated at 22! Insteadof the spray or spray plus packing, bubble plates or other suitablecontacting equipment may be used in zone 240.

The main advantage of this scrubber arrangement is the separation of thelarge amount of water needed for the cooling job in the top part of thetower from the small amount which is desired to use for slurry formationin the lower part of the tower. The temperatures and flow rates quotedare to be considered merely as examples and not as limitations of theinvention.

The apparatus described produces from the hot dust laden gases a largequantity of relatively cool and dry gases which may be used in anydesired process (for example, it may be compressed conveniently) and awater slurry of convenient concentration which may be withdrawn throughline 27% and returned to the process from which the solids wererecovered.

If it is desired to prevent the sedimentation or adsorbtion of solidwater impurities on the process solids located in number 210 a washer ofthe type illustrated in Figure 3 may be used to cooperate with scrubbingtower 219 of Figure 2 in the following manner.

It will be appreciated that considerable makeup water must be added tothe system of Figure 2 to supply that water which is evaporated in theatmospheric cooling towers. The heat of evaporation of this water mustequal the entire sensible heat removal between the hot feed gas, thecooled exit gas, and the condensed water leaving the scrubber. Inaccordance with the modification shown in Figure 3, no water is injectedinto the hot feed gas in line 2li5 of Figure 2 and the gas is cooledfrom say about 600 F. to about 230 F. by evaporation of water in thebubble trays 230. The slurry is withdrawn through line 270 as shown inFigure 2 and passed into a cone bottom vessel 310 shown in Figure 3. Inthis vessel the solid particles comprising the dust recovered from thegas stream, are washed by an upward rising current of pure condensatewater supplied through manifolds 315. The slurry from the bottom of theconeshaped vessel 310 is fed into a stream of condensate water in line220 and this stream is sent back to the process relatively free of solidimpurities contained in the water used in the cooling system. Sufiicientmakeup water of the ordinary type may be used in the cooling system toprevent deposition of dissolved particles in any part of the apparatus.The makeup water may be heated and passed through settling tanks forremoval of temporary hardness if desired.

It has been mentioned above that the metal oxide used may also actas acatalyst for the oxidation reaction. It will be understood that thereaction may be further catalyzed by the addition of extraneousoxidation catalysts such as vanadium oxide, or reformation catalystssuch as nickel. Reformation catalyst may be admixed with and circulatedtogether with the metal oxide to the reaction zones, 30, 40, 70, and 80to cause therein reformation of any CO2 formed with methane to formadditional amounts of CO and H2.

If appreciable amounts of CO2 are formed the product gas may becontacted with unconverted or freshly added quantities of methane orother gaseous hydrocarbons in the presence of a reforming catalyst inorder to produce a mixture of carbon monoxide and hydrogen by the wellknown reforming reaction. This reaction may take place in spaces 16 and62 above dense phase levels 14 and 6 the reforming catalyst being addedto the system in a relatively small particle size so that it will remainabove the bed of oxidation material, or it may be carried out in aseparate vessel, methane or the like being supplied to these spaces inany suitable manner.

A system adapted to carry out this latter type of process isschematically illustrated in Figure 4. This system essentially comprisesa methane oxidizer 41% a metal reoxidizer 430 and a reformer 45%.Oxidizer 410 contains a dense bed 412 of metal oxide such as iron oxidefluidized by the gaseous hydrocarbon to be oxidized, such as methane,supplied through line 414. Reoxidizer 43% is arranged in an elevatedposition with respect to oxidizer 41% and contains a dense bed 432 ofreduced metal oxide in the state of reoxidation and fluidized by airsupplied through line 434. Reformer 450 may be in an intermediateposition and holds a dense bed 452 of finely divided reformer catalystsuch as nickel or nickel supported by vanadium pentoxide or a carriersuch as kaolin, kieselguhr, magnesia or the like, fluidized byhydrocarbon gas supplied through line 453 and gaseous oxidation productsfrom oxidizer 410, supplied through line 456. Oxidizer 410 and reformer450 may be maintained at an elevated pressure of say about 75-200 lbs.per square inch, preferably about 100-150 lbs. per square inch, whilereoxidizer 43 3 is preferably kept at a lower pressure, preferably atabout atmospheric to 50 lbs. per square inch pressure.

Reoxidized metal oxide flows under the pressure of dense phase 432 andstandpipe 435 provided with a bottom control valve 43%, substantially atthe temperature of bed 432, into oxidizer 410, is reduced therein by thegaseous hydrocarbon and returned through the reverse standpipe 416provided with a top control valve 418 under the pressure of oxidizer 410to reoxidizer 430. Control valve 418 may also be placed lower in reversestandpipe 416, in which case aeration gas is supplied to 416 through oneor more taps 2 above such lower valve, particularly during the startingperiod.

About 25% or more of the hydrocarbon gas to be used in the entireprocess of synthesis gas production may be charged to oxidizer 410through line 414 to react with the metal oxide furnished throughstandpipe 436. When copper oxide is used substantially complete reactionto form CO2 and water vapor results. With iron oxide some CO and He willbe formed as well. The overhead gases from oxidizer 410 are then passedinto the reformer 450. In addition to the gases from vessel 410 the restof the methane to be used in the process is also charged to vessel 450through lines 453 and 454. Reaction between the water vapor and CO2 fromoxidizer 410 with the added methane results in the production of thedesired synthesis gas.

One of the problems in this process is to remove the heat of oxidationfrom oxidizer 410 and to supply the heat required in the reformation inreformer 450. To accomplish this, oxidizer 410 is operated at atemperature higher than reformer 450, say higher by about 50-100 F. ormore, and spent metal powder from oxidizer 410 may be circulated toreformer 450 to supply heat to this vessel and returned to oxidizer 410where it absorbs the heat released in the latter vessel. As shown inFigure 4, a withdrawal well 420 and standpipe 422 for reduced metaloxide to be transferred from oxidizer 410 to reformer 450 through line453, is located as far as possible from the end of standpipe 436 whichcharges the oxidized powder from the reoxidizer 430. It is one of theobjects of this invention to provide a method of transferring the heatbetween vessels 410 and 450 while at the same time transferring aslittle oxidized metal as possible from 410 to 450 where combustion of COand H2 would occur. The feed to a standpipe 458, by means of whichsolids may be returned from reformer 450 to oxidizer 410, through line460, may be elutriated by a stream of methane as indicated in thedrawing at 454. In this way the transfer '10 of reformer catalyst from450 to 410 may be minimized. This transfer, while not fatal to theprocess in small amounts, is to be avoided so that the reformer catalystmay be kept as active as possible.

The amount of reduced metal oxide transferred from oxidizer 410 toreformer 450 should be as small as possible and should not exceed theamount required for the desired heat supply to reformer 450. In manycases, the

' extent of reforming to be done in reformer 450 may be relatively sosmall that the heat supplied by the exit gases from oxidizer 4 10 may besuflicient and a solids circulation from oxidizer 410 to reformer 450may be substantially or completely dispensed with.

Operating temperatures may be about l5001900 F., preferably about 1700 Fin reoxidizcr 430; about l400l800 F., preferably about 1600 F., inoxidizer 410; and about 13001700 F., preferably about 1500 F. inreformer 450. If desired fresh metal or metal oxide may be supplied toreoxidizer 430 through line 435 and metal oxide fines of undesirablysmall size may be discarded through line 417. Similarly, fresh reformingcatalyst may be fed through line 451 to reformer 450 and spent materialwithdrawn from the system through line 457. The solids flow throughstandpipe 436 and 458 may be facilitated by the supply of small amountsof suitable fiuidizing gases through taps t as indicated.

While the operation of the systems illustrated by the drawing has beendescribed with reference to the production of carbon monoxide andhydrogen from natural gas or methane it will be understood that thissystem may be readily adapted by one skilled in the art to otheroxidation reactions such as the production of alcohols, aldehydes, acidsor other oxygenated compounds from gaseous or vaporous hydrocarbons.

Our invention will be further illustrated by the following specificexample:

Example For the production of about 3.50 million cu. ft. per day ofhydrogen and carbon monoxide in the approximate ratio of 1.9 mols ofhydrogen per mol of carbon monoxide from methane using cupric oxidehaving an average particle size of about 350 mesh as the oxidizing agentin a system of the type illustrated by Figure 1 the followingapproximate conditions have been found suitable.

Feed gas composition CH4=96.0%; CO2=4.O%. Reaction temperature 1520 F.Average reaction pressure 100 lbs. per sq. in. Regeneration temperature1620" F. CH4 fed rate 1.7 million cu. ft. per day. Air feed rate 4.5million cu. ft. per day. Solids circulation rate 18,000 lbs. per min.Superficial gas velocity in reactor 5 ft. per sec. Density of suspensionin reactor -l20 lbs. per cu. ft. Density of suspension in regenerator20022O lbs. per cu. ft.

The synthesis gas produced at these conditions has a composition aboutas follows:

While the foregoing description and exemplary operations have served toillustrate specific applications and results of the invention, othermodifications obvious to those skilled in the art are within the scopeof the invention. Only such limitations should be imposed on theinvention as are indicated in the appended claims.

What is claimed is:

1. In the production of gas mixtures containing carbon monoxide andhydrogen by the oxidation of gaseous hydrocarbons essentiallyexclusively with finely divided metal oxides in an oxidizing zone andreoxidation of metal oxide reduced in said oxidizing zone with air in areoxidation zone in a systemoperated by the fluid solids techniquewherein a dense turbulent bed of finely divided metal oxide fluidized byupwardly flowing gases to resemble a boiling liquid having a Welldefined upper level is maintained in said reoxidation zone, theimprovement which comprises supplying heat of reaction to said oxidizingzone as sensible heat of reoxidized metal oxide circulated from saidreoxidation zone to said oxidizing zone and operating said reoxidationzone at a higher temperature and a substantially lower pressure thansaid oxidizing zone.

2. The method as claimed in claim 1 in which the gases produced in saidoxidizing zone are subjected to reformation with at least one mildom'dizing agent selected from the group consisting of CO2 and steam inthe presence of a reformation catalyst.

3. The method as claimed in claim 1 in which said metal oxide at thereoxidation temperature has an oxygen partial pressure of less thanabout 0.10 atmosphere at equilibrium with both higher and lower stagesof oxidation.

4. In the method of producing mixtures of carbon monoxide and hydrogen'by oxidizing gaseous hydrocarbons in an oxidizing zone with metaloxides, reoxidizing reduced metal oxide with air in a reoxidizing zoneand reforming gaseous hydrocarbons with gaseous products of completeoxidation of gaseous hydrocarbons in a re forming zone in the presenceof a reforming catalyst, the improvement which comprises maintainingdense turbulent beds of finely divided oxidized and reduced metal oxidefluidized by upwardly flowing gases to resemble boiling liquids havingWell defined upper levels in said oxidizing and reoxidizing zones and asimilar fluidized bed of finely divided reforming catalyst comprisingreduced metal oxide in said reforming zone, operating said oxidizingzone at a pressure higher than that of said reoxidizing zone and atconditions conducive to the formation of substantial amounts of productsof complete oxidation including CO2 and water, maintaining a negativetemperature gradient from said reoxidizing zone to said oxidizing zoneto said reforming zone, supplying heat of reaction to said oxidizingzone as sensible heat of metal oxide circulated from said reoxidizingzone and heat of reaction to said reforming zones as sensible heat ofreduced metal oxide circulated from said oxidizing zone, supplyinggaseous hydrocarbons to said reforming zone, returning reduced metaloxide from said reforming zone to said oxidizing zone and from saidoxidizing zone to said reoxidizing zone and recovering carbon monoxideand hydrogen from said reforming zone.

References Cited in the file of this patent UNITED STATES PATENTS1,899,184 De Simo Feb. 28, 1933 1,957,743 Wietzel et a1. May 8, 19342,425,754 Murphree et a1 Aug. 19, 1947 2,631,094 Seymonds Mar. 10, 1953FOREIGN PATENTS 10,759 Great Britain of 1887 12,155 Great Britain of1892

1. IN THE PRODUCTION OF GAS MIXTURES CONTAINING CARBON MONOXIDE ANDHYDROGEN BY THE OXIDATION OF GASEOUS HYDROCARBONS ESSENTIALLYEXCLUSIVELY WITH FINELY DIVIDED METAL OXIDES IN AN OXIDIZING ZONE ANDREOXIDATION OF METAL OXIDE REDUCED IN SAID OXIDIZING ZONE WITH AIR IN AREOXIDATION ZONE IN A SYSTEM OPERATED BY THE FLUID SOLIDS TECHNIQUEWHEREIN A DENSE TURBULENT BED OF FINELY DIVIDED METAL OXIDE FLUIDIZED BYUPWARDLY FLOWING GASES TO RESEMBLE A BOILING LIQUID HAVING A WELLDEFINED UPPER LEVEL IS MAINTAINED IN SAID REOXIDATION ZONE, THEIMPROVEMENT WHICH COMPRISES SUPPLYING HEAT OF REACTION TO SAID OXIDIZINGZONE AS SENSIBLE HEAT OF REOXIDIZED METAL OXIDE CIRCULATED FROM SAIDREOXIDATON ZONE TO SAID OXIDIZING ZONE AND OPERATING SAID REOXIDATIONZONE AT A HIGHER TEMPERATURE AND A SUBSTANTIALLY LOWER PRESSURE THANSAID OXIDIZING ZONE.